The present invention relates generally to electronic components such as connectors, switches and sensors for conducting electrical current. More particularly, the invention relates to a method for manufacturing such components.
Electronic components in the form of a pultruded composite member having a plurality of small generally circular cross section conductive fibers embedded in a polymer matrix, where the fibers are oriented in a direction parallel to the axial direction of the member and are continuous from one end of the member to the other end of the member so as to have a fibrillated brush-like structure are known. The devices described are particularly well suited for low energy electronic/microelectronic signal level circuitry typified by contemporary digital and analog signal processing practices. Typical of the types of machines which may use such electronic devices are electrostatographic printing machines.
In electrostatographic printing apparatus commonly used today, a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image contained within the original document. Alternatively, a light beam may be modulated and used to selectively discharge portions of the charged photoconductive surface to record the desired information thereon. Typically, such a system employs a laser beam. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developer powder referred to in the art as toner. Most development systems employ developer which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development, the toner particles are attracted from the carrier particles by the charged pattern of the image areas of the photoconductive insulating area to form a powder image on the photoconductive area. This toner image may be subsequently transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure.
In commercial applications of such products, the photoconductive member has typically been configured in the form of a belt or drum moving at high speed in order to provide high speed multiple copying from an original document. Under these circumstances, the moving photoconductive member must be electrically grounded to provide a path to ground for all spurious currents generated in the electrostatographic process. This has typically taken the form of a ground strip on one side of the photoconductive belt or drum which is in contact with a grounding brush made of conductive fibers. Some brushes suffer from a deficiency in that the fibers are thin in diameter and brittle and therefore the brushes tend to shed. This can cause a problem in particular with regard to high voltage charging devices in automatic reproducing machines. If a shed conductive fiber comes into the contact with the charging wire, it has a tendency to arc causing a hot spot on the wire resulting in melting of the wire and breaking of the corotron. This is destructive irreversible damage requiring unscheduled service on the machine by a trained operator. In addition, the fiber can contaminate the device and disrupt uniformity of the corona charging.
Furthermore, in commercial applications of such products, it is necessary to distribute power and/or logic signals to various sites within the machine. Traditionally, this has taken the form of utilizing conventional wires and wiring harnesses in each machine to distribute power and logic signals to the various functional elements in an automated machine. In such distribution systems, it is necessary to provide electrical connectors between the wires and components. In addition, it is necessary to provide sensors and switches, for example, to sense the location of copy sheets, documents, etc. Similarly, other electrical devices such as interlocks, etc. are provided to enable or disable a function.
The most common devices performing these functions have traditionally relied on metal-to-metal contacts to complete the associated electronic circuitry. While this long time conventional approach has been very effective in many applications, it nevertheless suffers from several difficulties. For example, one or both of the metal contacts may be degraded over time by the formation of an insulating film due to oxidation of metal. This film may not be capable of being pierced by the mechanical contact forces or by the low energy (5 volts and 10 milliamps) power present in the circuit. This is complicated by the fact that according to Holm, Electric Contacts, page 1, 4th Edition, 1967, published by Springer-Verlag, if the contacts are infinitely hard, no amount of force can force contact to occur in more than a few localized spots. Further, corroded contacts can be the cause of radio frequency interference (noise) which may disturb sensitive circuitry. In addition, the conventional metal to metal contacts are susceptible to contamination by dust and other debris in the machine environment.
In an electrostatographic printing machine, for example, toner particles are generally airborne within the machine and may collect and deposit on one or more such contacts. Another common contaminant in a printing machine is a silicone oil which is commonly used as a fuser release agent. This contamination may also be sufficient to inhibit the necessary metal to metal contact. Accordingly, direct metal to metal contact suffers from low reliability particularly in low energy circuits. To improve the reliability of such contacts, particularly for low energy applications, contacts have been previously made from such noble metals as gold, palladium, silver and rhodium or specially developed alloys such as palladium nickel. For some applications, contacts have been placed in a vacuum or hermetically sealed. In addition, metal contacts can be self-destructive and will burn out since most metals have a positive coefficient of thermal conductivity. Therefore, as the contact spot gets hot due to increasing current densities, it becomes more resistive thereby becoming hotter with the passage of additional current and may eventually burn or weld. Final failure may follow when the phenomena of current crowding predominates the conduction of current. In addition to being unreliable as a result of susceptibility to contamination, traditional metal contacts and particularly sliding contacts, owing to high normal forces, are also susceptible to wear over long periods of time.
Therefore, it has become recently known to provide a non-metallic pultruded composite member having a plurality of small generally circular cross section conductive fibers in a polymer matrix, the fibers being oriented in the matrix in the direction substantially parallel to the axial direction of the member and being continuous from one end of the member to the other to provide a plurality of electrical point contacts at each end of the member with at least one end of the member having a fibrillated brush-like structure such that the plurality of fibers provide a densely distributed filament contact. The terminating ends of the fibers in the brush-like structure define an electrically contacting surface. One of the difficulties with manufacturing such fibrillated pultruded electronic components has been in making thin disk-like elements from a pultruded carbon fiber rod such that the disks can be sized to fit into existing switch packages. Difficulties have been encountered with mechanically cutting the rod into thin disks since the polymer matrix is heated and softened but then recondenses around the ends of the fibers thereby preventing the necessary fibrillated brush-like structure at the end of the disk. Laser cutting of such pultruded carbon fiber rods into thin disks has similarly proven difficult because the fibers conduct heat and the heat burns away the matrix from around the fibers even at distances removed from the plane of the laser cut.
Another reason why cutting such thin disks has been difficult is that while pultruded fibrous structures have a high degree of mechanical strength along the axis of the fibers in the pultrusion, they have poor radial strength and can be readily split or peeled apart. This is especially evident when using such pultruded rods in thin disk form so that they can fit within conventional switch packages. In such a structure, the disk is larger in diameter than in axial height and therefore has poor mechanical strength radially.
Accordingly, it has been considered desirable to develop a new and improved apparatus and process for manufacturing a fibrillated pultruded electronic component as a thin disk or the like which would overcome the foregoing difficulties and others while providing better and more advantageous overall results.